1. Field of the Invention
This invention relates to semiconductor device manufacturing and particularly to processes for shaping a surface of a semiconductor substrate for fabrication of an integrated micromachine sensor.
2. Description of Related Art
Local oxidation (LOCOS) processes are well known for forming thick (typically 5000 .ANG. to 10,000 .ANG.) oxide isolation areas known as field oxide. In a typical LOCOS process, a silicon nitride layer formed on the surface of a silicon substrate is patterned to create openings which expose parts of the substrate. The substrate is then heated in the presence of oxygen to grow the field oxide in the openings. The nitride layer is then be stripped, and conventional integrated circuit elements such as transistors are formed in and on areas of the substrate separated from each other by the field oxide.
Micromachines such as accelerometers and pressure sensors which have mechanical elements can be integrated with conventional circuit elements on silicon substrates. Forming such micromachines often requires shaping the surface to the substrate to form depressions and/or cavities. Some methods for forming depressions and cavities etch a silicon substrate, for example, with a potassium hydroxide (KOH) isotropic silicon etch or dry plasma etching, but these procedures typically leave residues, rough surfaces, or defects that make surfaces unsuitable for active integrated circuit elements or fusion bonding. Accordingly, methods for forming smooth, defect-free contoured surfaces are sought.